Protective covering of leather



Feb. 11, 1958 R. P. HOFFERBERT ETAL 2,823,157

PROTECTIVE COVERING OF LEATHER 2 Sheets-Sheet 1 Filed Jan. 21, 1953 John P Szumski William LD. McKay R..P. HOFFERBERT ETI'AL PROTECTIVE COVERING LEATHER Feb. 11, 1958 2 Sheets-Sheet 2 Filed Jan. 21, 1953 I- r 1 I 0 E55? 22 5 a 5? I (i 6g1 amr/ E Inventors Raymond]? Hoffrbezb John P Szumski mu bm lcxqy" H 2,823,157 1C Patented Feb. 11,1958

PROTECTEVE COVERING OF LEATHER Raymond P. Hoflerhert, Beverly, John P. Szumski, Salem,

and William L. D. McKay, Marblehead, Mass., assignors to United Shoe Machinery Corporation, Flemington, N. J., a corporation of New Jersey Application January 21, 1953, Serial No. 332,162

6 Claims. (Cl. 154-131) This invention relates to the protection of leather and particularly relates to improved protected leather pad covers for resilient pads for applying pressure to the soles of shoes and to methods for making such pad covers.

Cement-sole-attaching machines employ yielding pads usually of rubber which apply pressure to soles through a flexible sheet known as a pad cover. Pad covers must be sufliciently flexible to transmit uniform pressure from the yielding pads to soles and at the same time must be resilient so that they will return to their original shape when pressure is relieved. Additionally, pad covers must have and retain a very smooth sole-engaging surface, must be waterproof and must be unaffected by solvents or cements used in sole attaching.

It has been proposed heretofore to provide a pad cover including a lower layer of leather and an exposed layer of polymerized vinyl chloride resin bonded to the leather by a layer of adhesive. In this combination pad cover, the leather provides resilience and strength which returns the pad cover substantially to its original shape when pressure is released; and the vinyl resin layer is relied upon to protect the leather.

While this known pad cover was eifective under the conditions prevailing at the time it was devised, changing conditions as to cement, solvents and activating conditions have created certain problems which are not solved by that pad cover. Thus, modern synthetic rubber cements and the very active solvents employed in connection with their use attack vinyl resins and these cements adhere to vinyl resins to an extent which causes relatively rapid destruction of the smooth surface of the vinyl resin layer. Deterioration of the vinyl resin layer permits moisture from tempered shoe soles to reach and harm the leather layer.

It is a feature of the present invention to protect leather, particularly a leather pad cover for a sole attaching press, bya layer of a resinous material united to and in fused engagement with the leather, the resin being substantially unaffected by the cements and solvents employed in modern shoemaking. w I It is a further feature to provide a method for combining resin and leather without the use of an intervening adhesive film.

' We have found that polyethylene resin may-be joined permanently to leather by a special heat. andvpressure treatment to form a fused-together composite sheet particularly adapted to withstand the destructive forces involvedin use of the material as a pad cover for a sole press. In the composite, the portions of the polyethylene adjacent to the leather layer flow into the irregularities of the leather surface and surround any projecting fibers of 'the leather to form a union'which is not ruptured by continued flexing or by abrading or stretching of the leather in use. The polyethylene is unafiected by the action of water or by present day solvents or cements used on the'shoe soles; likewise, becauseof the intimate relation between the leather layer and the thin layer of polyethylene resin, the polyethylene resin is supported and reinforced to an extent such that it is not disrupted or destroyed by continued abrasive action of the shoe soles bent and formed in the press.

The invention will be further described with the ac companying drawings forming part of the disclosure.

In the drawings:

Fig. l is a plan view of a layer of leather having an outline, shape and size to cover and protect a pad of a sole-attaching machine;

Fig. 2 is an angular view illustrating an optional impregnation treatment for the surface of the leather layer of Fig. 1;

Fig. 3 is an angular view illustrating the assembly of a layer of polyethylene resin with the leather layer of Figs. 1 or 2;

Fig. 4 is a fragmental view illustrating the step of joining the polyethylene resin layer with the leather layer under heat and pressure;

Fig. 5 is an enlarged view with portions exaggerated to illustrate the joint in the fused composite of polyethylene resin and leather;

Fig. 6 is a sketch on microscopic scale of the joint between the polyethylene and the leather;

Fig. 7 is an angular view of a composite pad cover for a profile sole-pressing pad; and

Fig. 8 is a sectional elevational view of a profile solepressing pad with a polyethylene protected leather pad cover secured in position for the molding of a sharply curved sole.

A primary field of utility of the present invention is in providing pad covers for pressure-applying pads of cement sole-attaching machines, and the following description will be concerned with this field; It will be understood that the process and composite sheet are susceptible of other uses.

Pad covers are essentially a flexible resilient sheet corresponding in size and shape to the surface of the pad to protect it from wear and from injury by cements or solvents, and sufiiciently flexible to transmit pressure uniformly from the pad to the shoe. A pad cover regularly supplied as an article of manufacture is a sheet 10 of leather having the outline shape shown in Fig. l. The forward portion 12 is shaped to cover the forepart section of a pad and has flange portions 14 which will extend beyond the edge of a pad and under a retainer to hold the forward portion in place during pressing operations. The shank portion 16 of the cover is normally of reduced width to enable the pad cover to be bent more sharply around and to mold the shank portion of a shoe sole, but is of suflicient width to protect the pad. The rear portion of the pad cover includes portions 18 which extend under a retainer to hold the pad cover in place.

A simple polyethylene-leather pad cover 20. according to the present invention may be prepared (see Fig. 3) by combining a layer 12 of leather preferably, but not new essarily cut to final shape, with a layer 22 of polyethylene and joining them in a press 24 (see Fig. 4) under conditions which will produce the novel fused together union, illustrated in Fig. 5, in whichzthe leather layer 12 and polyethylene arecombined in aspecial cooperativerrelar -tio'nship.- .In this uniongthe leather layer 12 backs up the thin layer of polyethylene 22 to resist mechanical damage to the polyethylene 22, and is the main source [of resilience and strength of the-pad cover 10, while a e polyethylene 22 provides a smooth solvent- ,and cementresistant shield penetrating atuleast the surface portions of the leather: 12 and serving-to protectthe leather 12 even when the polyethylenefsurfac'e'22 is scarredas by upstanding tacks ina' shoe-bottom, i

12 under pressure and at a temperature which for a brief perlod is above the melting point of the polyethylene. The heat softened polyethylene is forced by the pressure into the surface of the leather and is then solidified by a rapid cooling.

The most satisfactory union of polyethylene 22 and leather 12 has been obtained using split chrome retan leather. The surface of this leather is readily penetrated by the hot fluid polyethylene and the leather is not injured by its brief exposure to the high temperature. Also this leather possesses the fiber firmness for reinforcement of the polyethylene against mechanical injury, and the strength, resilience and flexibility required in a pad cover.

Other leathers, preferably but not necessarily chrome tanned, may be used. Where a grained leather is employed, it is desirable to bufi its surface prior to combination with the polyethylene resin in order to improve penetration and to secure a better union between the polyethylene film and the leather base. For fiat pad covers, leathers up to nine irons in thickness may be used. For profile pads it is preferred to use four to six iron leather.

The ethylene polymers used in the present invention are those having a high molecular weight ranging from about 18,000 to 30,000, preferably from about 19,000 to 23,000 and may have a melting point of about 230 F. The toughness of the polyethylene may be increased if desired by milling a small amount, e. g., about 2% of a carbon black, such as acetylene black, .with the polyethylene.

In an optional procedure, shown in Fig. 2, useful to improve the bond, particularly where a grained leatheris used, the surface of the leather layer 12 may be treated with a not solution of polyethylene resin in a solvent, such as toluene or xylol, for example by applying the solution with a brush 26 to form a polyethylene deposit 28. The temperature of the solution should be high enough to dissolve polyethylene but below the boiling point of the solvent, e. g. a temperature of about 93 C., was found useful for a solution in toluene. Preheating the leather to a temperature above 60 C. and preferably to about 75 C., but below values which would harm the leather, improves penetration of the solution. This treatment introduces polyethylene below the surface of the leather and this polyethylene fuses with the polyethylene layer 22 on the surface of the leather 12 during the hot pressing to give a depth to the union of polyethylene resin 22 with the leather 12 which might not otherwise be obtained in the combination of polyethylene resin with grained leather.

The leather layer 12, whether treated with polyethylene resin solution or not, is assembled with a layer 22 of polyethylene resin sheet material as shown in Fig. 3 and the assembly is disposed between the platens 30 and 32 of a press 24 (Fig. 4). The upper platen 30, i. e., the platen bearing against the polyethylene layer 22 is provided with heating and cooling means, shown as thin walled conduits 34 for the circulation of steam or cold water by which the platen 30 may be raised to operating temperature and may be cooled rapidly after fusing of the polyethylene. I

To secure a strong permanent union between the polyethylene 22 and the leather 12 it is important to bring the temperature of the polyethylene 22 up to within about 5 to 15 F. below the softening point of the polyethylene and at the same time to heat the surface of the leather 12 to substantially the same temperature prior to fusing and pressing the polyethylene 22 into union with the leather 12. In this heating, caution must be taken to avoid heat injury to the leather. This is best accomplished by keeping the surface of the platen 32 on which the leather 12 rests in cool condition and by maintaining the heated surface of the upper platen out of pressure contact with the polyethylene 22 during this first heating stage. That is, it is believed that with the leather 12 in uncompacted condition, transmission of heat from its upper surface to its interior portions is substantially less than if the leather were compacted and hence the danger of burning the body of the leather is less than if this first heating stage were conducted with the assembly under pressure. It is also believed that the surface of the leather 12 remains in better condition, i. e., with its pores open, for union with the polyethylene if mechanical pressure is not applied while the polyethylene 22 and leather 12 are cool. An effective technique for carrying out this first heating is to move the platens 30 and 32 of the press together until the upper platen 30 is just in pressureless contact with the polyethylene layer 22 and then to heat the upper platen 30 as by circulation of steam through the conduits 34 to a temperature which may be from 30 to 50 or more above the melting point of the polyethylene. Under these conditions the temperature of the polyethylene 22 is raised to the desired point without substantial melting in a period of from two to five minutes.

When the first stage of heating is completed, i. e., when the polyethylene 22 and leather 12 have reached a temperature of from 5 to 15 below the softening point of the polyethylene, a high pressure, which may be from 50010 600 lbs. per square inch, is applied to the assembly and serves to melt the polyethylene 22 and force it into the surface of the leather 12. As soon as pressure has been established, the upper platen 30' is cocled as rapidly as possible by circulation of cooi water through the c0nduits'34 to harden the polyethylene resin and to prevent heat damage to the leather. The cooling of the platen 30 to-1 0 P. is usually completed in from 1 /2 to four minutes. The platens 3t": and 32 of the press are then separated and the composite polyethylene leather sheet 36 is removed. Inspection of the composite sheet 36 showed that the portions of the original polyethylene sheet 22 projecting eyond the leather 12 had not been fused by the treatment but that in all portions where the polyethylene 22 was in contact Withthe leather 12 and hence in pressure contact with the platen 32, the polyethylene had been fused and pressed into the surface of the leather. Examination of a cross section of the polyethylene leather sheet (see Figs. 5 and 6) shows that the polyethylene 22 had flowed into the surface irregularities of the leather to form teeth-like projections 38 firmly holding the polyethylene 22 onto the leather 12 while the free surface 40 of the polyethylene 22 had beenpressed to a smooth fiat surface.

This fused-together polyethylene resin and leather sheet 36 may be used in this form as a protective cover for pads of the fiat type, i. e., where the pads press against relatively shallow curved portions on the shoe sole.

For the molding of more sharply curved soles, as for example in the molding of soles of womens shoes, the flat composite sheet 36 is subjected to a further treatment to form a so called profile pad cover 42 (see Fig. 7) which is used with a profile pad 44 and pad box 46 as shown in Fig. 8. The outline of the profile pad cover 42 is somewhat difierent from that of the fiat type of pad cover 20, and comprises a forward portion 48having a width sufficient to extend under a retainer or mask plate 50 at the edges of the pad. The shank portion 52 is substantially narrower to permit the pad to assume a more sharply curved shape and to Wrap around the shank portion of a sole. The back portion 54 of the pad cover is provided with portions 56 wider than the shank portion'52 adapted to extend under a retainer, usually in the form of clips 58 to prevent displacement of the back portion 54 of the pad cover. A composite sheet of leather and polyethylene resin for use in a profile pad cover 42 is formed by uniting a layer of leather 12a having the shape above described with a sheet of polyethylene resin 22a by the same procedure employed in forming a flat pad cover-20 described above. After removal from the pressand trimming oil? the excess polyethylene from the edges, the leather 12a is moistened and the composite is placed in a metal forming mold to impart to it a contour corresponding to the working faces of the parts of a profile sole-pressing pad 44. Briefly, this contour involves a relatively deep curved portion 60 in the shank area 52 and an angular relationship between the shank portion 52 and the forward and back portions 48 and 54 of the pad cover 42. After forming of the composite to the desired contour, the composite is removed from the press and the leather 12a is permitted to dry. The exposed back of the leather 12a is secured by cement, which may be a conventional synthetic rubber sole-attaching cement, to a molded rubber part 64 having a contour corresponding to the shape of the work faces of the parts of the sole-pressing pad 44. The rubber part 64 has a projection 66 on its bottom portion for engagement with a recess 68 in the sole-pressing pad 44 to aid in holding the pad cover 42 in alinement with the pad 44.

As shown in Fig. 8, the composite cover 42 thus prepared is positioned on a profile sole-pressing pad with the rubber projection 66 disposed in the recess 68 in the pad 44, with the margin at the forward portion 48 of the pad cover retained beneath a mask plate 50, and with the margin 56 of the back portion 54 disposed beneath clips 58 at the back portion of the sole-pressing pad 44. The sole-pressing pad 44 is supported in a pad box 46 including an articulated metal frame 70 and a fluid filled rubber container 72 directly underlying the sole-pressing pad 44. When a shoe is pressed against the pad cover 42, the pad 44 is compressed and the fluid in the container 72 is displaced from points of greatest pressure so that the pad cover 42 is Wrapped around and uniformly pressed against the sole of the shoe. This wrapping involves a very substantial change in the contour of the pad cover 42 and subjectsthe union of the polyethylene 22a and leather 12a to substantial stress which would tend to rupture any but the strongest connection between the leather and the polyethylene.

The following example is given to aid in understanding the invention but it is to be understood that the invention is not restricted to the specific materials given in the example. I Example.A chrome retan leather flesh side split, 6 irons in thickness, was cut to form a leather piece 12a having an outline comparable to that shown in Fig. 7 comprising a relatively wide forward portion 48 for engagement by a mask plate 50 on a sole-pressing pad 44, a shank portion 52 of reduced width and a back portion 54 having margins 56 for engagement by retainer clips 58. This leather piece 12a was disposed on the bottom platen 32 of a press, and a sheet 22a of polyethylene resin (melting point 230 F.) 15 mils in thickness was disposed on its surface. The top platen 30 of the press was brought into pressureless contact with the polyethylene and was raised in a period of 2 /2 minutes to a temperature of 290 F. (as taken by a pyrometer) by circulation of steam through passages 34 in the platen. At this point the temperature of the polyethylene and adjacent leather surface was 218 F. The assembly of leather 12a and polyethylene 22a was then subjected to a pressure of 500 pounds per square inch. Cooling water was circulated through the passages 34 in the upper platen 30 as soon as pressure was established. The temperature was reduced to 100 F. in 2 /2 minutes, the press was opened, the leather-polyethylene composite was removed and the polyethylene projecting beyond the edges of the leather was stripped ofi.

The leather 12a was then wet with water and was placed in a preforming mold to shape it to the desired contour. The contour involved a relatively deep curve 60 in the shank portion 52 and an angular relation between the shank portion 52 and the forward portion 48 and the back portion 54 of the composite. The composite was then removed from the mold and dried overnight. The back of the leather piece 12a was then coated with a conventional synthetic rubber sole-attache ing cement and permitted to dry to a tacky state. A molded vulcanized rubber part 64 shaped as a backing for the composite leather-polyethylene component and having a projection 66 on its bottom surface was coated on the surface opposite the projection with sole-attaching cement which was also allowed to dry to a tacky state. The leather-polyethylene composite and the molded rubber part 64 were placed together with their cemented surfaces in contact and pressed together under a pressure of 400 lbs. After 20 seconds, pressure was released and the finished pad was taken from the press.

Under standard factory conditions involving its use with a pad 44 and a pad box 46, as shown in Fig. 8, this pad cover was still in excellent condition after 100,000 cycles of operation.

Having described our invention, what we claim as new and desire to secure by Letters Patent of the United States 1. The method of protecting leather which comprises the three step process of first disposing a thin sheet of high molecular weight polyethylene on a surface of a leather sheet and heating the polyethylene sheet and substantially said surface only of the leather sheet to a temperature near but below the melting point of the polyethylene, secondly pressing a heated surface simultaneously against all areas of the sheet of polyethylene to be joined to said leather surface tomelt the polyethylene to fluid condition and toforce the hot fluid polyethylene into the surface of the leather, said heated surface having a temperature substantially above the melting point of the polyethylene, and thirdly cooling the heated surface promptly after establishing pressure to reduce the temperature of the surface to a point well below the melting temperature of the polyethylene and thereafter releasing said pressure. p

2. The method of protecting leather which comprises the steps of first applying to the surface of the leather a solution of polyethylene resin in a volatile organic solvent and evaporating the solvent, secondly disposing a thin sheet of high molecular weight polyethylene having a molecular weight of from 18,000 to 30,000 on the polyethylene-treated surface of the leather and'heating the polyethylene sheet and substantially said treated surface only of the leather sheet to a temperature near but below the melting point of the polyethylene, thirdly pressing a heated surface simultaneously against all areas of the sheet of polyethylene to be joined to said leather'surface to melt the polyethylene sheet and to force the hot fluid polyethylene into the irregularities in the surface of the leather and cause the fluid polyethylene to unite with the polyethylene in the surface of the leather, said heated surface having a temperature substantially above the melting point of the polyethylene, and finally cooling the heated surface promptly after establishing pressure to reduce the temperature of the surface to a point well below the melting temperature of the polyethylene and thereafter releasing said pressure.

3. The method of protecting leather which comprises the three step process of first disposing a thin sheet of high molecular weight polyethylene having a molecular weight of from 18,000 to 30,000 on a surface of a chrome retan split leather sheet and heating the polyethylene sheet and substantially only said surface of the leather to a temperature from 5 to 15 F. below the melting point of the polyethylene, secondly pressing a heated surface simultaneously against all areas of the sheet of polyethylene to melt the polyethylene and to force the hot fluid polyethylene into the surface of the leather, said heated surface having a temperature at least 30 F. above the melting point of the polyethylene, and said heated pressure to reduce the temperature of the surfaceto a.

point well below the melting temperature of the polyethylene and thereafter releasing said pressure. I l

4. The method of forming a protected'leather cover for a yielding elastic pad which comprises the steps of first disposing a thin sheet of high molecular weight polyethylene having a molecular weight of 18,000 to 30,000 on a surface of a chrome retan split leather sheet and heating the polyethylene sheet and substantially only said surface of the leather to a temperature from to 15 F. below the melting point of the polyethylene, secondly pressing a heated surface simultaneously against all areas of the sheet of polyethylene to be joined to said leather surface to melt the polyethylene and to force the hot fluid polyethylene into the surface of the leather, said heated surface having a temperature at least 30 F. above the melting point of the polyethylene, and said heated surface being pressed against the polyethylene with a pressure of from 500 to 600 lbs. per square inch, thirdly cooling the heated surface promptly after establishing pressure to reduce the temperature of the surface to a point Well below the melting temperatureof the polyethylene and thereafter releasing said pressure, and finally moistening said leather layer, molding the polyethylene leather composite to a contour corresponding to the contour of the elastic pad for which the composite is to serve as a cover, and drying the leather while retaining the contour imparted to the composite.

5. The method of protecting leather cover material for a yielding elastic pad which comprises the three step process of first disposing a to 20 mil sheet of high molecular weight polyethylene having a molecular weight of from 18,000 to 30,000 on the working surface of a chrome retan split leather sheet and heating the polyethylene sheet and substantially only said surface of the leather at a rate to raise the temperature of the polyethylene andleather surface to 5 to F. below the melting point of the polyethylene in a period of 2 to 4 minutes, secondly pressing a heated surface simultaneously against all areas of the sheet of polyethylene to be joined to said leather surface to melt the polyethylene and to force the hot fluid polyethylene into the surface of the leather, said heated surface having a temperature approximately 50" F. above the melting point of the polyethylene, and said surface being pressed against the polyethylene with a pressure of 500 to 600 lbs. per square inch, and thirdly cooling the heated surface promptly after establishing pressure to reduce the temperature of the surface to a point well below the melting temperature of the polyethylene in aperiod of not over 4 minutes and thereafter releasing said pressure.

6. The method of forming a protected leather cover for a yielding elastic pad which comprises the steps of first disposing a 1.0 to 20 mil sheet of high molecular weight polyethylene having a molecular Weight of from 18,000 to 30,000 on the Working surface of a chrome retan split leather sheet and heating the polyethylene sheet and substantially only said surface of the leather at a rate to raise the temperature of the polyethylene and leather surface to 5 to 15 F. below the melting point of the polyethylene in a period of 2 to 4 minutes, secondly pressing a heated surface simultaneously against all areas of the sheet of polyethylene to melt the polyethylene and to force the hot fluid polyethylene into the surface of .the leather, said heated surface having a temperature approximately 50 F. above the melting point of the polyethylene, and' said surface being pressed against the polyethylene With a pressure of 500 to 600 lbs. per square inch, thirdly cooling the heated surface promptly after establishing pressure to reduce the temperature of the surface in a period of not over 4 minutes to a point well below the melting temperature of the polyethylene and thereafter releasing said pressure, fourthly moistening said leather layer, molding the combined polyethylene and leather to a contour corresponding to the contour of the working face of the elastic pad for Which the composite is to serve as a cover and drying the leather while retaining the contour imparted to the composite and finally adhesively securing to the exposed face of the leather layer a layer of vulcanized rubber having a contour corresponding to the contour of the working face of said elastic pad.

References Cited in the file of this patent UNITED STATES PATENTS 1,208,209 Prince Dec. 12, 1916 2,032,471 Conant Mar. 3, 1936 2,070,600 Ienett Feb. 16, 1937 2,219,700 Perrin et al. Oct. 29, 1940 2,236,766 Schneider Apr. 1, 1941 2,358,404 Lennon Sept. 19, 1944 2,413,750 Davis Jan. 7, 1947 2,462,331 Myers Feb. 22, 1949 2,564,424 Chadbourne Aug. 14, 1951 2,622,052 Chandler Dec. 16, 1952 2,622,056 De Coudres et a1 Dec. 16, 1952 FOREIGN PATENTS 641,568 Great Britain Aug. 16, 1950 

1. THE METHOD OF PROTECTING LEATHER WHICH COMPRISES THE THREE PROCESS O FIRST DISPOSING A THIN SHEET OF HIGH MOLECULAR WEIGHT POLYETHYLENE SHEET AND SUBLEATHER SHEET AND HEATING THE POLYETHYLENE SHEET AND SUBSTANTIALLY SAID SURFACE ONLY OF THE LEATHER SHEET TO A TEMPERATURE NEAR BUT BELOW THE MELTING POINT OF THE POLYETHYLENE, SECONDLY PRESSING A HEATED SURFACE SIMULTANEOUSLY AGAINST ALL AREAS OF THE SHEET OF POLYETHLENE TO BE JOINED TO SAID LEATHER SURFACE TO MELT THE POLYETHYLENE TO FLUID CONDUCTION ON TO FORCE THE HOT FLUID POLYETHYLENE INTO THE SURFACE OF THE LEATHER, SAID HEATED SURFACE HAVINGA TEMPERATURE SUBSTANTIALLY ABOVE THE MELTING POINT OF THE POLYETHYLENE, AND THIRDLY COOLING THE HEATED SURFACE PROMPTLY AFTER ESTABLISHING PRESSURE TO REDUCE THE TEMPERATURE OF THE SURFACE TO A POINT WELL BELOW THE MELTING TEMPERATURE OF THE POLYETHYLENE AND THEREAFTER RELEASING SAID PRESSURE. 